Dynamics of variable dusk–dawn flow associated with magnetotail current sheet flapping
<p>We present Cluster spacecraft observations from 12 October 2006 of convective plasma flows in the Earth's magnetotail. Earthward flow bursts with a dawnward <span class="inline-formula"><i>v</i><sub>⊥<i>y</i></sub></span> compon...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2021-12-01
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| Series: | Annales Geophysicae |
| Online Access: | https://angeo.copernicus.org/articles/39/1037/2021/angeo-39-1037-2021.pdf |
| Summary: | <p>We present Cluster spacecraft observations from 12 October 2006 of
convective plasma flows in the Earth's magnetotail. Earthward flow bursts
with a dawnward <span class="inline-formula"><i>v</i><sub>⊥<i>y</i></sub></span> component, observed by Cluster 1 (C1), are
inconsistent with the duskward flow that might be expected at the
pre-midnight location of the spacecraft. Previous observations have
suggested that the dusk–dawn sense of the flow can be governed by the
interplanetary magnetic field (IMF) <span class="inline-formula"><i>B</i><sub><i>y</i></sub></span> conditions, with the related
“untwisting hypothesis” of magnetotail dynamics commonly invoked to explain this dependence, in terms of a large-scale magnetospheric asymmetry. In the current study, observations of the upstream solar wind conditions from OMNI, magnetic field observations by Cluster and ionospheric convection data using SuperDARN indicate a large-scale magnetospheric morphology consistent with positive IMF <span class="inline-formula"><i>B</i><sub><i>y</i></sub></span> penetration into the magnetotail. At the pre-midnight location of Cluster, however, the dawnward flow observed below the neutral sheet by C1 could only be explained by the untwisting hypothesis in a negative IMF <span class="inline-formula"><i>B</i><sub><i>y</i></sub></span> scenario. The Cluster magnetic field data also reveal a flapping of the magnetotail current sheet, a phenomenon known to influence dusk–dawn flow. Results from the curlometer analysis technique suggest that the dusk–dawn sense of the <span class="inline-formula"><strong><em>J</em></strong>×<strong><em>B</em></strong></span> force was consistent with localised kinks in the magnetic field and the flapping associated with the transient perturbations to the dusk–dawn flow observed by C1. We therefore suggest that the flapping overcame the dusk–dawn sense of the large-scale convection which we would expect to have been net duskward in this case. We conclude that invocation of the untwisting hypothesis may be inappropriate when interpreting intervals of dynamic magnetotail behaviour such as during current sheet flapping, particularly at locations where magnetotail flaring becomes dominant.</p> |
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| ISSN: | 0992-7689 1432-0576 |